974 



THE ORGANS OF DIGESTION. 



stomach ; let two layers of cloth attached to the posterior border represent the 

 mesogastrium attached to the vertebral column (Fig. 598). This was the original 

 condition (Fig. 592). Now turn the stomach to the right, allowing the cloth to 

 fall loosely to the left, and immediately a cavity is formed included between two 

 layers of cloth anteriorly and two layers posteriorly (Fig. 599). In the embryo 

 a similar cavity is formed called the cavity of the great omentum, the lesser sac 

 of peritoneum, bursa omentalis ; and a similar fold of four layers is formed called 

 the great omentum which in the embryo and infant contains this cavity. 



The entrance to this cavity is indicated by the arrow in Figs. 595, 596, and 

 599, and the bulging of the great omentum is seen to the left of and below the 

 greater curvature of the stomach. Compare the above with Fig. 600, and the 

 position of the sac will be better understood. 



The front wall of the bursa omentalis is formed by the stomach ; the posterior 

 wall by the mesogastrium, which at first completely invests the pancreas, touches 

 the spleen, and covers part of the left suprarenal capsule. The opening is turned 

 to the right and covered anteriorly by the lesser omentum. The space between 



Right 



suprarenal 



captule 



Liver 



Right 



suprarenal 



capsule 



Left 



supraienal 

 capsule 



Liver 



FIG. 600. Schematic and enlarged cross section 

 through the body of a human embryo in the region 

 of the mesogastrium. Beginning of third month. 

 (Toldt.) 



Left 



suprarenal 

 capsule 



Liver 



FIG. 601. Same section as in Fig. 600, at end of 

 third month. (.Toldt.) 



the lesser omentum and right end of pancreas is the atrium bnrsa? omentalis or 

 the antechamber or lesser omental pocket. It lies below and behind the Spigelian 

 lobe of the liver. The bursa proper, or lesser sac, is that part behind the stomach. 



By the end of the third month the pancreas touches the left suprarenal cap- 

 sule (Fig. 601), the layer of mesogastrium separating the two becomes later 

 absorbed, and the pancreas is then an extraperitoneal organ separated from the 

 kidney or capsule by connective tissue. By further development this lesser sac 

 continues to push between the layers of the great omentum downward and to the 

 left, and fuses with neighboring viscera. The great omentum, formerly a part 

 of the mesogastrium, comes to hang freely down over the transverse colon and 

 then in front of the small intestines, as about to do in Figs. 596 and 602. 



The lamellae composing the bursa omentalis or lesser sac are each composed 

 of two layers ; they are placed close together and are continuous below (Figs. 

 602 and 603). The more anterior one is attached to the greater curvature of 

 the stomach and the posterior one lying on the intestines was originally attached 

 to the vertebral column and enclosed most of the pancreas (Figs. 600 and 602). 

 In many mammals no further change occurs. In man fusions follow : the pos- 



